This invention relates generally to transducers and in the preferred embodiment relates to a pressure unit assembly for use in measuring the oil pressure of an automobile engine.
There are many instances where it is desirable to convert fluid pressure into a signal to convey pressure information to an observer or operator. For example, in the automotive field, an oil pressure unit may be mounted on the engine in communication with the outlet of the oil pump to monitor the pump pressure and convey an indication of this pressure to the operator of the vehicle. For example, one way of communicating this information is via an electric signal which is supplied from the pressure unit to an electrical gage on the vehicle's instrument panel. The gage displays an indication of the oil pressure to the vehicle operator.
The basic idea of a pressure unit is well known. A typical pressure unit comprises a pressure responsive element, often a flexible diaphragm, which is placed in communication with the sensed pressure. Within the pressure unit is a variable impedance whose effective impedance is a function of the movement of the pressure responsive element, and thus is an indication of sensed pressure. The prior art contains various patents disclosing this basic type of structure.
U.S. Pat. No. 2,439,092 in the name of Linstrom discloses a resistive element deposited in spiral fashion on one face of a flexible diaphragm. A spherical contoured contact element is adjustably spring biased toward, and in juxtaposition to, the face of the diaphragm which contains the spiral resistive element. The diaphragm is placed in communication with a source of pressure to be monitored, and the diaphragm is flexed in accordance with the sensed pressure to selectively engage the spiral resistive element with the spherically countoured contact element in an amount which is a function of the sensed pressure. In this way, selected portions of the resistive element are short circuited thereby providing an effective resistance of the unit which is indicative of sensed pressure.
U.S. Pat. No. 4,079,351 in the name of Levine discloses a pressure unit for use in sensing oil pressure in which a diaphragm is communicated to the pressure source and operatively coupled with a variable resistance. Calibration is by means of an adjusting screw.
U.S. Pat. No. 2,244,958 in the name of Moross discloses a pressure unit in one embodiment of which the resistive element is disposed on a convex contour, and the contact element is operated by a diaphragm device in cantilever fashion relative to the convex resistive element to thereby selectively short circuit the turns of the resistive element.
U.S. Pat. No. 3,080,757 in the name of Johansson discloses a pressure unit in which resistive elements are disposed on a flexible diaphragm and the diaphragm is selectively flexed against juxtaposed contact elements as a function of sensed pressure. This patent is similar to the Linstrom patent in that the resistive elements are disposed on the flexible diaphragm. A possible disadvantage of this type of construction is that the resistive elements might have a tendency toward failure because they must flex with the flexible pressure responsive diaphragm.
U.S. Pat. No. 2,867,769 in the name of Hunt et al discloses a pressure unit wherein a convexly curved spring element forms the contact element which selectively engages a wound resistor element. A calibration screw engages the spring element.
U.S. Pat. No. 3,445,801 in the name of Sattler discloses a pressure responsive unit containing a helically wound resistive element which is itself helically arranged within the pressure unit. A contact structure is operated by the pressure responsive diaphragm to selectively short circuit the turns of the resistive element to provide the pressure indicating signal.
U.S. Pat. No. 2,466,846 in the name of Giesler discloses a pressure responsive device where a convex surface is rocked against a wound resistor element to selectively short circuit turns of the resistor in providing the pressure indicating signal.
U.S. Pat. No. 1,683,059 in the name of Van Deventer discloses a variable resistance in which a shorting bar of convex contour is selectively shorted against a resistor bar as a function of the displacement of the contact bar. This latter patent discloses simply a resistor structure and is not shown in the context of a pressure unit assembly.
The present invention provides a number of significant improvements over the prior art as represented by the foregoing patents. One feature of the invention is that it provides an improved spring contact and resistor structure which offers convenient and accurate calibration in conjunction with good response and sensitivity, but without excessive manufacturing cost. The resistor is a separate unit which is inserted into a portion of the pressure unit body. The resistor has a convex surface on which the resistor wire is disposed. A spring contact element is provided within the unit and has a main contact portion generally diametrically disposed in relation to the axis of the unit and in juxtaposition to the convexly disposed resistor wire. The spring contact element is operatively coupled with a pressure responsive diaphragm to be urged against the resistor wire with increasing pressure. As the pressure increases, the amount of engagement of the spring contact elements with the resistor wire increases thereby short circuiting an increasing number of turns to provide a signal indication of sensed pressure. The spring contact element further includes projections which engage selective locations within the body of the unit. These projections bear against the unit's body to aid in supporting the spring contact element during its flexing against the resistive element. In the preferred embodiment the projections project away at 90.degree. angles from opposite sides of the main contact portion. The distal end portion of one projection bears against a pad fashioned on the interior of the transducer body. The distal end of the opposite projection bears against the tip of a calibration screw which is threaded into a threaded bore on the transducer body. The calibration screw may be adjusted externally of the pressure unit to position the distal end of the projection and in this way the flexing characteristics of the spring contact element are varied by the setting of the adjustment screw and this in turn provides a calibration function whereby the unit may be conveniently and accurately calibrated externally of the unit. While external calibration adjustments are not per se new in the context of pressure units, the instant arrangement provides a novel and unique structure which is not seen to be present in the prior art described above. Moreover, the spring contact and resistor arrangement represents new and unique structure not to be found in this prior art.
A further significant feature of the pressure unit of the present invention is that the terminal arrangement is of improved constuction. In this regard, the resistor element which was indicated to be a separate unit above, includes intermediate electrical terminals which are embedded in the core on which the resistive element is disposed. The ends of the resistive element are electrically joined by suitable means to the portions of the intermediate terminals which are embedded in the resistive core. During assembly of the resistor into the body of the pressure unit, pressure termination occurs between intermediate terminal and external terminals and it is unnecessary to be concerned about making connections for the ends of the resistive wire to other portions of the unit structure. Furthermore, one external terminal, (ungrounded) and the body are configured such that when the resistor is assembled into the body that external ungrounded terminal projects through a corresponding aperture in the wall of the body so as to become available externally of the unit for connection to an external electrical circuit. The other external terminal (the ground side) extends from the other intermediate terminal within the body and projects through a corresponding aperture in the wall of the body so as to become secured in electrical contact with the electrically conductive fitting via which the pressure unit mounts on an engine. This fitting is threaded into a corresponding tapped hole in the engine and provides a passage via which pressure is communicated to the diaphragm, and the fitting provides a ground path to the engine. Prior art patents above do not disclose a terminal arrangement of this type.
A further feature believed to be unique not only in the context of a pressure transducer but more generally in resistor devices per se is the resistor structure which includes on the convex core surface a notch within which a portion of the resistive element is disposed. By so locating a portion of the resistor within the notch, the signal provided by the unit can exhibit a larger initial step. This particular feature is not disclosed in any of the above-mentioned patents.
Further features of the invention include its less complex construction than many other types of commercial pressure units. It is adapted for automated fabricated and can be manufactured on a much more competitive basis. The pressure unit also makes efficient use of material and has weight advantages. Other ancillary features which will be described in more detail hereinafter also contribute to improvements in the pressure unit.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention in accordance with the best mode presently contemplated in carrying out the invention.